UPS fan working,when it shouldn't
I have an old Accupower 1400VA UPS.
Still works fine,but the last couple years it started doing something annoying.
The fan used to work only when the power was out,and the batteries were running.So unless there was a power shortage it was dead silent.
Now the fan starts working on its own at random moments,without a power shortage,and because it's a 60mm fan,it makes a lot of noise.It doesn't have to do with load,as it may work while it's idle,or while it's at load.
It usually does this at day.At night it rarely works.
What could it be?
I'm thinking of opening it and cleaning it up a bit,as after almost 10 years it will be dusty.Also replace the thermal paste at the mosfets.
Another solution is to just replace the fan with a 80mm silent one.I have 3d printed an 60 to 80 mm adapton already.
The batteries are ok ,as I measured them and they keep the pc at idle,almost 50 minutes.They are the same type as the original.